Many off road machines with automatic transmissions have an alternate start gear (typically second gear) besides first gear. And many of these automatic transmissions are equipped with a first gear lock out feature that prevents the transmission from operating in first gear while the gear shift lever is set in the normal drive (D) mode. In these machines, first gear only becomes available if the gear shift lever is set in a lower gear, such as D1 or D2.
A benefit of having a transmission with an alternate start gear is that it eliminates the time it takes to shift from first to second gear. Also, shifting from first to second gear can take so much time, sometimes three quarters to one and a quarter seconds, that it interrupts machine acceleration, especially in large heavy duty off road trucks.
U.S. Pat. No. 6,676,566 discloses a control system for a machine with an automatic transmission which sets a second starting shift position in a lower gear relative to a first shift position and then automatically changes from the first to the second shift position when a slow running intention is detected. The control system has a manual mode in which the driver can indicate a slow running intention and an automatic mode in which the shift position is automatically selected. Unlike the present invention, the invention disclosed in the '566 patent does not include a standard/default start gear and does not automatically downshift to an alternative (lower) start gear if conditions might otherwise cause the machine to have inadequate performance, including inhibiting the machine from moving forward.
It would therefore be beneficial to provide a system and method for controlling an automatic transmission having an alternate forward start gear in which the control system can sense from various environmental and machine conditions when more power is needed and cause the transmission to automatically downshift.